Many different tools used in the oil exploration and production industry utilize bodies or components comprising matrix materials which are exposed to very abrasive and erosive environments. For example, earth boring bits are used in various applications in the earth drilling industry which typically have very abrasive and erosive environments. Earth boring bits have bit bodies which include various features such as a core, blades, cutter pockets that extend into the bit body, and gage pads on a bit body, for example. Depending on the application/formation to be drilled, the appropriate type of drill bit may be selected based on the cutting action type for the bit and its appropriateness for use in the particular formation. In PDC bits, polycrystalline diamond compact (PDC) cutting elements are received within the bit body pockets and are typically bonded to the bit body by brazing to the inner surfaces of the pockets. Bit bodies are typically made either from steel or from a tungsten carbide matrix bonded to a separately formed reinforcing core made of steel.
Matrix bit bodies are typically formed of a single, relatively homogenous composition throughout the bit body. The single composition may contain a single form of hard particles such as a tungsten carbide or a mixture of hard particles such as different forms of tungsten carbide. The matrix material is commonly bonded into solid form by fusing a metallic binder material (binder phase) and the hard particles (hard particle phase, e.g., carbide phase).
The drill bit formation process typically includes placing a matrix powder material within a mold. The mold is commonly formed of graphite and may be machined into various suitable shapes with features that correspond generally with desired exterior features of the resulting matrix drill bit body. Displacements are typically added within the mold to define the cutter pockets. Other formers may also be added to the mold to define other features such as nozzles/ports, internal hydraulic fluid flow passages, external hydraulic fluid flow passages (i.e., junk slots), etc. The matrix powder material may be a powder of a single material such as tungsten carbide, or it may be a mixture of more than one material such as different forms of tungsten carbide. The matrix powder material may include further components such as supplemental metal additives. An infiltrating metal binder material is then typically placed over the matrix powder material. The components within the mold are then heated in a furnace to the flow or infiltration temperature of the binder material at which temperature the melted binder material infiltrates the tungsten carbide or other matrix material. The infiltration process that occurs during sintering (heating) bonds the particles (grains) of matrix material to each other and to the other components to form a solid bit body. The sintering process also causes the matrix material to bond to other structures that it contacts, such as a metallic blank core which may be suspended within the mold to produce the aforementioned reinforcing core. After formation of the bit body, a protruding section of the metallic blank core may be welded to a second component called an upper section. The upper section typically has a tapered portion that is threaded onto a drilling string. The bit body typically includes blades which support the PDC cutting elements which, in turn, perform the cutting operation. The PDC cutting elements are bonded to the body in pockets in the blades, which are cavities formed in the bit for receiving the cutting elements.
The infiltrated matrix materials determine the mechanical properties of the bit body. These mechanical properties include, but are not limited to, transverse rupture strength (TRS), toughness (resistance to impact-type fracture), hardness, wear resistance and/or erosion resistance from rapidly flowing drilling fluid and abrasion from rock formations, steel bond strength between the matrix material and steel reinforcing elements, such as a steel blank, and strength of the bond to the cutting elements, i.e., braze strength, between the finished body material and the PDC cutter.
Typically, a single matrix powder is selected in conjunction with the infiltration binder material, to provide desired mechanical properties to the bit body for ease of manufacturing. The single matrix powder is packed throughout the mold cavity to form a bit body having the same mechanical properties throughout. It would, however, be desirable to optimize the overall structure of the drill bit body by providing different mechanical properties to different portions of the drill bit body, in essence tailoring the bit body. For example, erosion and/or wear resistance is especially desirable at regions proximate the cutting elements and/or throughout the outer surface of the bit body while high strength and toughness are especially desirable in the interior portions of the bit body such as the bit blades and throughout the bulk of the bit body. However, when using a single matrix powder to form the bit body, changing a matrix material to increase erosion and/or wear resistance usually results in a corresponding loss in toughness, or vice-versa.
Further, in packing the matrix powder materials into the mold, the geometry of the bit (and thus mold) make it difficult and time-consuming to place different matrix materials in different regions of a bit body. When using different powdered matrix materials, there is little or no control over powder locations in the mold during assembly, particularly around curved and vertical surfaces. When using a paste of the matrix material and organic binder, it is extremely time-consuming to position the paste by hand in the desired locations to the desired thickness.
Accordingly, there exists a continuing need for developments in matrix tool bodies to improve the erosion and/or wear resistance of the tool body without compromising the strength/toughness of the tool body and without increasing the difficulty of the manufacturing process.